Speaker 1: Hey there, listeners, this is Jonathan. Before we get into
Speaker 1: the episode, I want to acknowledge something. Uh. Twitter user
Speaker 1: Charlie Tango Bravo helpfully pointed out that I made a mistake.
Speaker 1: When we first published this episode, I completely misrepresented the
Speaker 1: inverse square law, and so later in this episode you
Speaker 1: will hear me kind of interrupt to give a proper explanation.
Speaker 1: My apologies for that. Uh and um, yeah, I mean,
Speaker 1: this one's totally on me. I made a mistake, and
Speaker 1: I feel real dumb about it. But you know, mistakes happen.
Speaker 1: It doesn't. It just tells me I need to be
Speaker 1: even more careful in the future to make sure that
Speaker 1: I'm not misrepresenting something, which I totally was in the
Speaker 1: original version of this episode. Anyway, let's get to the episode,
Speaker 1: and when we get to the part where I'll correct it,
Speaker 1: I'm pretty sure we'll be apparent. Enjoy. Welcome to Tech Stuff,
Speaker 1: a production from I Heart Radio. Hey there, and welcome
Speaker 1: to tech Stuff. I'm your host, Jonathan Strickland. I'm an
Speaker 1: executive producer with I Heart Radio and I love all
Speaker 1: things tech and listener Terry A. Carlson, and I apologize
Speaker 1: for very likely Butchering your name, asked if I might
Speaker 1: cover how space vehicles navigate. So we're going to talk
Speaker 1: about navigation, and this is one of those things I
Speaker 1: find really fascinating and also sometimes frequently actually a bit confusing.
Speaker 1: Now I blame part of that confusion on my own
Speaker 1: fascination with stuff like Star Wars, which some folks call
Speaker 1: science fiction. I think of it as fantasy that happens
Speaker 1: to be set in space, or even Star Trek, which
Speaker 1: is closer to science fiction than Star Wars, but can
Speaker 1: play a bit fast and loose with science and technology.
Speaker 1: And these kind of properties gave me a really cool
Speaker 1: but an accurate feel for how space navigation works. Terry,
Speaker 1: you asked that I cover what references and methods do
Speaker 1: space programs used to actually do space navigation? And that's
Speaker 1: a great question, because all of this really does rely
Speaker 1: on reference or relationships between a vehicle and something else,
Speaker 1: Like it's all relative. You know, we're going to talk
Speaker 1: about that a lot in this episode. And I guess
Speaker 1: on some level this is intuitive, but I had not
Speaker 1: really thought about it in concrete terms before. So, for example,
Speaker 1: here on Earth, if you're giving directions to someone, you
Speaker 1: would tell that person how to get to a place
Speaker 1: relative to where they are right now, Right, I mean,
Speaker 1: the same thing holds true for space vehicles. But we've
Speaker 1: got to remember that everything in space is moved ing
Speaker 1: all the time. So here on Earth, if you need directions,
Speaker 1: you can start from a position in which you know
Speaker 1: you're not moving relative to the Earth. You're standing still.
Speaker 1: On Earth, You're still moving, but that's because the arts moving.
Speaker 1: We're going to get to that. And you know you're
Speaker 1: standing still with reference to the Earth. But in space,
Speaker 1: everything is moving in reference to everything else. Now you
Speaker 1: could be moving at a similar velocity relative to your surroundings.
Speaker 1: So from your perspective, it might seem like you're not
Speaker 1: all really moving together, but trust me, you totes are.
Speaker 1: Now what I'm about to go into it really matters
Speaker 1: when we start thinking about the possibility of traveling beyond
Speaker 1: our solar system to another. But it's it's, you know,
Speaker 1: something that we have to take into consideration, even when
Speaker 1: we're talking about travel within our Solar system. So let's
Speaker 1: start with the easiest stuff first and then work our
Speaker 1: way up. The Earth travels in a nearly circular orbit
Speaker 1: around the Sun, right, I mean, this is not news
Speaker 1: to you. I imagine. So the Earth is moving, it's
Speaker 1: moving in an orbital path around the Sun. The orbit
Speaker 1: moves at a speed that's around sixty thousand miles per
Speaker 1: hour if you prefer, that's about or almost thirty kilometers
Speaker 1: per second. Now, if we're talking about going to space
Speaker 1: to do stuff in low Earth orbit, we're pretty much
Speaker 1: thinking to Earth, right, We're not too worried about everything
Speaker 1: else that's going on. The orbital speed of Earth isn't
Speaker 1: as big a deal in that case, we don't have
Speaker 1: to take that into as much account. But let's say
Speaker 1: that we want to travel to Mars. Go from Earth
Speaker 1: to Mars. Well, Mars is further out from the Sun
Speaker 1: than Earth, right, I mean it goes my very educated mother.
Speaker 1: So Mars comes after Earth. Oh, in case you've not
Speaker 1: actually heard that mnemonic device, this is how I learned it.
Speaker 1: It was my very educated mother just served us nine pickles.
Speaker 1: That stands for Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune,
Speaker 1: and Pluto the planets except well, you know, when I
Speaker 1: was a kid, Pluto was a planet, and then Pluto
Speaker 1: kind of got the boot as far as being a
Speaker 1: planet goes. So I guess now you could say, my
Speaker 1: very educated mother just served us nothing. Thanks mom. Okay. So,
Speaker 1: Mars is further out from the Sun than Earth is,
Speaker 1: and Mars's orbit is obviously a bigger circle around the
Speaker 1: Sun than Earth's orbit is, because you know, Mars is
Speaker 1: further out from the center of our solar system. Mars
Speaker 1: also doesn't have the same orbital velocity as Earth. Earth
Speaker 1: completes one orbit of the Sun every three sixty five
Speaker 1: Earth days, with a little bit of change leftover. That's
Speaker 1: why we have to have leap years, and Mars's orbit
Speaker 1: is just a hair under six hundred eighty seven Earth
Speaker 1: days long. But beyond that, Mars's orbital velocity is closer
Speaker 1: to twenty kilometers per second. Remember Earth's is closer to
Speaker 1: thirty kilometers per second. So Mars is not just moving
Speaker 1: in a greater distance because it's orbit is larger, it's
Speaker 1: moving a little slower compared to Earth, you know, and
Speaker 1: again relative to the Sun. So that means if we
Speaker 1: want to plot a course from Earth to Mars, we
Speaker 1: have to take all that into account, right, because we
Speaker 1: can't travel instantaneously. It takes time for us to get
Speaker 1: from point A to point B. We can't just point
Speaker 1: a rocket at where Mars appears to be to us
Speaker 1: right at that moment and then launch the rocket in
Speaker 1: that direction. You know, look at the sky, find the
Speaker 1: red dot and say aim that away, because you know,
Speaker 1: the positions of Earth and Mars are shifting in their orbits,
Speaker 1: and Mars will not be at that same spot by
Speaker 1: the time the vehicle we launch gets there. Heck, it's
Speaker 1: not even at that spot as we look at it,
Speaker 1: because it takes time for light to travel from Mars
Speaker 1: back to us, So we're really looking at where Mars
Speaker 1: used to be, and we would be shooting a rocket
Speaker 1: at where Mars used to be a really long time ago. Uh.
Speaker 1: The vehicle it would take months to travel there, so
Speaker 1: by the time it would get to that position in space,
Speaker 1: Mars wouldn't be there anymore. By the way, all this
Speaker 1: orbital stuff is why when we talk about sending a
Speaker 1: crew of human astronauts to Mars, we talk about missions
Speaker 1: that typically are on the order of a couple of
Speaker 1: years in length. The trip from Earth to Mars could
Speaker 1: take around eight months, and that's if we time it
Speaker 1: so that the launch vehicle UH shoots the spacecraft up
Speaker 1: and has the spacecraft travel the least amount of distance
Speaker 1: needed in order to go from Earth to Mars. That
Speaker 1: means you're timing it right. You're aiming at where Mars
Speaker 1: is going to be, and you want to time it
Speaker 1: so that Earth and Mars are at one of the
Speaker 1: closest points in their respective orbits to one another. You
Speaker 1: out of time it just right. And because of the
Speaker 1: difference in orbital velocities and the fact that mars Is
Speaker 1: year is significantly longer than Earth's year, that means that
Speaker 1: by the time you would arrive on Mars, Earth and
Speaker 1: Mars would no longer be super close together anymore. Right
Speaker 1: Like they're they're constantly in motion, so now they're moving
Speaker 1: apart from each other. That means for you to get
Speaker 1: back to Earth, you would need way more fuel for
Speaker 1: your return trip than you did for your trip out
Speaker 1: to Mars. Potentially, so the most fuel efficient thing to
Speaker 1: do is to hunker down on Mars and do all
Speaker 1: your science e stuff and you wait for the planets
Speaker 1: to reach a point in their orbits where again you
Speaker 1: will be traveling the least amount of distance you can
Speaker 1: get away with. And all told, that means a mission
Speaker 1: needs to last around two years to get all that done.
Speaker 1: Plus you know, theoretically you could even spend some of
Speaker 1: that time on Mars making rocket fuel, so you wouldn't
Speaker 1: necessarily have to carry all of it with you on
Speaker 1: the way there. Anyway, that's just a simple example of
Speaker 1: how motion in space matters. But we're just getting started, right,
Speaker 1: So I've touched on stuff like low Earth orbit and
Speaker 1: interplanetary travel within a solar system. But it's not just
Speaker 1: that the planets are moving around the Sun. Our entire
Speaker 1: Solar system is hurtling through space. We are part of
Speaker 1: the Milky Way Galaxy, and at the center of the
Speaker 1: Milky Way Galaxy there is a super massive black hole
Speaker 1: that's kind of the you know, it's like the Sun
Speaker 1: is in our Solar system, except there's a supermassive black
Speaker 1: hole in the middle of a galaxy billions of solar systems.
Speaker 1: Scientists estimate that our galaxy has somewhere between a hundred
Speaker 1: to four hundred billion stars in it. So think about that.
Speaker 1: I can't. I tried, but that's just a number that's
Speaker 1: just way too big for me to even get a
Speaker 1: rudimentary grasp on it. Anyway, our solar system is traveling
Speaker 1: in its orbit in the galaxy at a speed of
Speaker 1: around four thousand miles per hour or two kilometers per second.
Speaker 1: Then we have to consider that our galaxy is also
Speaker 1: in motion. We've got other neighboring galaxies in our neighborhood
Speaker 1: is just part of a super cluster of galaxies, and
Speaker 1: that in itself is part of an even bigger super cluster.
Speaker 1: And we're all hurtling through space at around a thousand
Speaker 1: kilometers per second. Where are we going? Well, I mean,
Speaker 1: I want to say, get in loser, we're going shopping,
Speaker 1: but we're not. We're headed to the Great Attractor. And
Speaker 1: to my surprise, that isn't Oscar Isaac. It's a gravitational
Speaker 1: point in the Lania Kia super cluster. Uh. And um,
Speaker 1: you know the Great Attractor is also moving towards another mass,
Speaker 1: the Shapley super Cluster. I guess there's always a bigger fish.
Speaker 1: And you know, we could keep going down this rabbit hole.
Speaker 1: But what I really wanted to point out is that
Speaker 1: we're talking about a lot of body ease in motion here,
Speaker 1: and that makes navigation more tricky, right, I mean, this
Speaker 1: is kind of like saying that you stop to ask
Speaker 1: for directions, but the town you stop in is actually
Speaker 1: moving on the map, and the place you're going to
Speaker 1: is also moving on the map. Maybe it's moving away
Speaker 1: from the town you are in, which is still in motion.
Speaker 1: So the route you are going to take to get
Speaker 1: there is changing by the minute. It gets complicated, so
Speaker 1: you have to take, uh, you know, into account a
Speaker 1: lot of things. You have to take reference points in
Speaker 1: order to make it all makes sense. And of course
Speaker 1: that's like talking about a map that's two dimensional. Obviously
Speaker 1: in space you're talking about three dimensional. You're not limited
Speaker 1: by a two dimensional plane. You're moving in three dimensional space. This,
Speaker 1: by the way, is all before we even consider stuff
Speaker 1: like relativity, which makes things even more weird. Einstein's theories
Speaker 1: of relativity really show how our universe behaves in ways
Speaker 1: that we don't often get to observe of directly. So
Speaker 1: we don't have a lot of direct perspective on these things.
Speaker 1: But let's use an example to explain some of relativity,
Speaker 1: and we'll start with special relativity. That's the I would
Speaker 1: argue the easier of the two to get a grasp on. Alright,
Speaker 1: so we've got two people and we're gonna name them
Speaker 1: Alice and Bob. Alice has superpowers, and Alice can travel
Speaker 1: through space without a space suit and can move at
Speaker 1: near the speed of light. So she flies through space
Speaker 1: close to the speed of light, and she goes and
Speaker 1: flies off on an adventure at top speed. When she
Speaker 1: comes back and she meets up with her best friend Bob,
Speaker 1: the two notice something unusual. So to Alice, it'll seem
Speaker 1: like Bob aged faster than normal, as if more time
Speaker 1: had passed for Bob than it did for Alice. To Bob,
Speaker 1: it will seem like Alice has aged less than normal,
Speaker 1: like not as much time passed for her, like like
Speaker 1: like less time pass less than it should have. And
Speaker 1: the reason for this is that the faster your speed
Speaker 1: is relative to some other reference point. This is why
Speaker 1: we talk about relativity. It is relative to some other
Speaker 1: reference point, the slower time will pass for you relative
Speaker 1: to that reference point. So again, like Bob is our
Speaker 1: our reference point for Alice. So it appears like, you know,
Speaker 1: Alice hasn't aged as much because time appeared to pass
Speaker 1: slower for Alice than it did to Bob. Now to Alice,
Speaker 1: time will have seemed to pass as normal for our
Speaker 1: own frame of reference. So in other words, it wouldn't
Speaker 1: feel to her as if time had slowed down. She
Speaker 1: would feel like time was passing, just as it would
Speaker 1: if she were standing perfectly still on Earth. A second
Speaker 1: would feel like a second to her. And in fact,
Speaker 1: if Alice were wearing a watch with a second hand,
Speaker 1: it would seem to be clicking one second at a time,
Speaker 1: just perfectly. Now, if Bob could somehow observe that watch
Speaker 1: while Alice is traveling at near the speed of light,
Speaker 1: Bob would see that the second hand is moving really slowly.
Speaker 1: It would be taking way longer than a second for
Speaker 1: it to take each tick. In fact, the faster you go,
Speaker 1: the slower it gets. And if you got to the
Speaker 1: point where you could travel at the speed of light,
Speaker 1: it would stop like the second hand wouldn't move anymore.
Speaker 1: For Bob, he wouldn't see the second If somehow Alice
Speaker 1: could move faster than the speed of light, which is
Speaker 1: as Einstein would put it impossible, it would look as
Speaker 1: though the second hand was going backwards. She would be
Speaker 1: traveling back in time. Now that's physically impossible. So I
Speaker 1: just thought I would throw head in there as an
Speaker 1: interesting you know, side note. But again to Alice, it
Speaker 1: would seem like time was passing as normal. And likewise,
Speaker 1: let's say Bob's wearing a watch. He has a second hand.
Speaker 1: To Bob, time is passing just as normal. A second
Speaker 1: takes a second, he can watch the little second hand
Speaker 1: click on buy on this on his watch. Now, let's
Speaker 1: say that Alice is able to see Bob's watch. While
Speaker 1: Alice is traveling at near light speed, it would look
Speaker 1: to her as if the second hand was going way
Speaker 1: too fast, like it was just spinning around the watch face.
Speaker 1: And again, Bob and Alice would each feel the passage
Speaker 1: of time as if it were just normal. It's only
Speaker 1: when they compare it to a point of reference, when
Speaker 1: they are relative to something else, that they see that
Speaker 1: there is any type of difference. Now, for most of
Speaker 1: our experiences on Earth, we don't notice this effect, and
Speaker 1: that's partly because we're usually traveling at a similar velocity
Speaker 1: relative to one another. We're all on this planet. Most
Speaker 1: of us aren't going super duper fast. However, there are
Speaker 1: cases where we can measure a difference. It wouldn't be
Speaker 1: observable like to our normal senses, but with very sensitive
Speaker 1: you know, metrics, we could see that there was a
Speaker 1: difference there. It's settled because we are not able to
Speaker 1: go anywhere close to the speed of light, at least
Speaker 1: not yet. So for example, we have the case of
Speaker 1: Mark and Scott Kelly. These are twin brothers who are
Speaker 1: both astronauts. Now, both of the Kelly's have spent time
Speaker 1: in orbit. Mark Kelly was born first, he's the older
Speaker 1: of the two twins, and he's logged fifty four days
Speaker 1: in space. Pretty respectable, right, I mean extremely respectable, Mr Kelly.
Speaker 1: I don't mean to, you know, dismiss that incredible achievement.
Speaker 1: But Scott Kelly has spent five hundred twenty days in orbit,
Speaker 1: almost ten times as much time in orbit, and a
Speaker 1: lot of that was aboard the International Space Station, which
Speaker 1: orbits the Earth at the speed of around twenty eight
Speaker 1: thousand kilometers per hour or seventeen thousand, five hundred miles
Speaker 1: per hour. So for a significant amount of time, Scott
Speaker 1: was traveling much faster relative to his brother Mark, who
Speaker 1: was back here on Earth. And since traveling faster means
Speaker 1: that time passes more slowly relative to an outside observer,
Speaker 1: it means that the gap between Mark and Scott actually
Speaker 1: got bigger. Mark aged faster here on Earth than Scott
Speaker 1: did out in space because of that speed of travel.
Speaker 1: Mark once said that he used to be six minutes
Speaker 1: older than his brother, but now, thanks to all that
Speaker 1: space travel that Scott did at high speeds, Mark is
Speaker 1: six minutes five milliseconds older. And that's a funny thing
Speaker 1: to say. Uh And sure you could argue, well, that's
Speaker 1: not really significant to our normal frame of reference. I mean,
Speaker 1: what's five milliseconds, But it does show that we actually
Speaker 1: have to keep this in mind when it comes to
Speaker 1: space travel. It does matter. Now when we come back,
Speaker 1: we're gonna tackle a little bit more of a relativity.
Speaker 1: But first let's take a relatively quick break. Okay, we're back,
Speaker 1: and we are not done with relativity yet. The speed
Speaker 1: and time thing is all part of special relativity. But
Speaker 1: Einstein was a real you know Einstein, and he also
Speaker 1: published his theory on general relativity. This includes an explanation
Speaker 1: that if you were to have two clocks and one
Speaker 1: of them is closer to a gravitational mass than the
Speaker 1: other one, the other one is much further out from
Speaker 1: that gravitational mass. The one that's closer to the gravitational
Speaker 1: mass will take more slowly than the one that's further out.
Speaker 1: This is separate from the whole you know, speed thing.
Speaker 1: So in other words, gravity also affects the rate at
Speaker 1: which time passes. It passes more slowly when you're closer
Speaker 1: to a big center of gravity. And this becomes really
Speaker 1: important for navigation just here on Earth, not even just
Speaker 1: space navigation, but navigation here. And you might wonder why
Speaker 1: that is. Well, a lot of us depend upon GPS
Speaker 1: apps or devices, right like we pull that up whenever
Speaker 1: we're going someplace new, and these devices they work by
Speaker 1: relying on signals that are coming from GPS satellites. It
Speaker 1: gets a few of these different signals and then it's
Speaker 1: able to pinpoint the location where on the surface of
Speaker 1: the Earth we happen to be at that given time. Well,
Speaker 1: those satellites are really far away from us. They are
Speaker 1: beyond low Earth orbit, so they're beyond where the International
Speaker 1: Space Station is, for example. They're out in medium Earth
Speaker 1: orbit somewhere around twenty two KOs out from the Earth,
Speaker 1: or around twelve fifty miles. So these satellites are much
Speaker 1: further out from the Earth's gravitational mass than say your
Speaker 1: watch or come on, we'll be real here your smartphone.
Speaker 1: So because of that, the clocks on the GPS satellites
Speaker 1: tick slightly fat stir. Then the clocks here on Earth tick. Remember,
Speaker 1: the closer you are to a gravitational mass, the slower
Speaker 1: time will pass for that particular frame of reference compared
Speaker 1: to a different frame of reference. I always have to
Speaker 1: throw that part in because again, in the moment it passes,
Speaker 1: the way time passes, like the way our experience of
Speaker 1: time is remains the same, not to our own frame
Speaker 1: of reference. Now, the GPS satellites are also traveling really
Speaker 1: fast relative to us, so that actually means that we
Speaker 1: have to take a bit off the top right, because
Speaker 1: we know that the faster you travel, the slower time
Speaker 1: uh affects you relative to someone who's not traveling at
Speaker 1: that speed. So the effects of general relativity mean that
Speaker 1: a clock on a GPS satellite has on average around
Speaker 1: forty five micro seconds more than an Earth clock at
Speaker 1: the end of a day, a full day. But again,
Speaker 1: because these satellites are link faster relative to us, the
Speaker 1: clocks also have a negative seven micro seconds two factor,
Speaker 1: and compared to our clocks, due to special relativity, so
Speaker 1: we have to combine those two together forty five and
Speaker 1: negative seven. That gives us thirty eight micro seconds that
Speaker 1: are extra on the GPS clocks. So if if we
Speaker 1: were to stop it right at midnight for both clocks,
Speaker 1: you know here on Earth and at the GPS satellite,
Speaker 1: we would see midnight on our clock and midnight plus
Speaker 1: thirty eight million micro seconds, not milliseconds micro seconds on
Speaker 1: the GPS side. Now, because our navigation depends upon taking
Speaker 1: signals from satellites and essentially measuring how long it took
Speaker 1: for that signal to go from the satellite to us,
Speaker 1: in order for us to calculate where we are on Earth,
Speaker 1: we actually have to account for that difference between our
Speaker 1: clocks and the satellite satellites clocks, or else we start
Speaker 1: to get some drift, and that means that over time,
Speaker 1: and and we're actually talking about years here, but it
Speaker 1: does happen, our navigation systems would become less accurate, which
Speaker 1: would eventually get to a point where our GPS device
Speaker 1: wouldn't even really show us where we are because it
Speaker 1: would be miscalculating based upon the the differences in the
Speaker 1: clocks on the GPS satellites versus the clock on our
Speaker 1: phone or that our phone is connected to, and instead
Speaker 1: it would show you where it thinks you are, but
Speaker 1: there would be a growing gap between where it thinks
Speaker 1: you are and where you really are. Based upon this
Speaker 1: gap in time. It would take like seven years for
Speaker 1: that to get to a point where we might even
Speaker 1: notice it, and we do correct for it. So essentially
Speaker 1: what happens is we shave thirty eight micro seconds off
Speaker 1: the clocks every midnight that the that the clock's hit.
Speaker 1: So when the clocks hit midnight on the GPS satellites,
Speaker 1: they kind of hold for thirty eight microseconds, which puts
Speaker 1: them I can sync with the clocks here on Earth.
Speaker 1: And then we have to do it every single day
Speaker 1: because every single day we get the effects of relativity.
Speaker 1: All right, well, that's something we have to take into
Speaker 1: account with navigation, Like these are things that we don't again,
Speaker 1: we don't necessarily have to think about here on Earth. Typically,
Speaker 1: most of us don't come into situations where special and
Speaker 1: general relativity have a noticeable impact on our day to
Speaker 1: day experience. UM. One really important element in space navigation
Speaker 1: is something called the deep Space Network, which is not
Speaker 1: a really cool science fiction channel, uh, no, it's it's
Speaker 1: actually a bunch of antennas, and it's it's more than that.
Speaker 1: But that's a big part of it. If we go
Speaker 1: back to the nineteen fifties, we had the space race
Speaker 1: ramping up. In nineteen fifty seven, the then Soviet Union
Speaker 1: launched spot Nick into orbit. The US was already working
Speaker 1: on its own satellite, and of course there were reasons
Speaker 1: for this beyond the scientific push. Scientific push was a
Speaker 1: big part of it, but there were other political reasons.
Speaker 1: For one thing, Demonstrating that you could put a payload
Speaker 1: into space also sent the message of hey, comrade, we
Speaker 1: can build rockets big enough to reach you, even though
Speaker 1: we're on the other side of the world, and you know,
Speaker 1: nuclear weapons are a thing, so you know, this wasn't
Speaker 1: just you know, a science thing. But that's another tangent
Speaker 1: that I won't go down any further. But on the
Speaker 1: U s side, one of the things that the Jet
Speaker 1: Propulsion Laboratory or JPL undertook was a job from the
Speaker 1: United States Army, which effectively you know, ran the jp
Speaker 1: L to establish radio tracking stations in certain parts of
Speaker 1: the world, including places like Singapore, Nigeria, and California. So upon,
Speaker 1: launching the first successful US satellite, which was called Explorer one.
Speaker 1: These ground stations would receive data from the satellite to
Speaker 1: be able to track it as it passed over overhead.
Speaker 1: This was essentially telemetry data, and you might wonder what
Speaker 1: does that mean. Well, telemetry is essentially the process of
Speaker 1: using some sort of device to measure something. It could
Speaker 1: be temperature, it could be pressure, it could be speed
Speaker 1: or velocity, and then it transmits that information to a
Speaker 1: distant receiver. Now, in this case, the telemetry was mostly
Speaker 1: about the Explorer one's orientation and velocity as it went
Speaker 1: through its orbit. Engineers at mission control could take that
Speaker 1: data and plot out the Explorer one's orbital path. In October,
Speaker 1: the US government established NASA, and this was really to
Speaker 1: consolidate the space efforts from various independent groups, mostly in
Speaker 1: the military, like the Army, Navy, and Air Force all
Speaker 1: had independent space exploration UH initiatives, so this was to
Speaker 1: kind of bring them all under one civilian umbrella and
Speaker 1: combine all those resources to be more effective. So this
Speaker 1: included the Jet Propulsion Laboratory that had previously been run
Speaker 1: by the U. S Army that became part of NASA.
Speaker 1: In December of nineteen and NASA would assign to the
Speaker 1: jp L the responsibility of planning out planetary and lunar
Speaker 1: exploration missions that would use unscrewed spacecraft, that is, spacecraft
Speaker 1: that did not have human beings abort robotic spacecraft if
Speaker 1: you prefer. Now. That would necessitate a network system of
Speaker 1: receivers here on Earth to be able to receive communications
Speaker 1: with and then to send communications too, as well as
Speaker 1: to just keep track of these robotic spacecraft as they
Speaker 1: traveled away from the Earth. You can't just have one
Speaker 1: really big antenna in Houston, because you know, the Earth
Speaker 1: rotates and sometimes Houston would be pointing the wrong way.
Speaker 1: Get together, Houston. So yeah, to establish that these antenna
Speaker 1: around the Earth need to be pointing outward in such
Speaker 1: a way that you have maintained contact with distant spacecraft. Moreover,
Speaker 1: as the spacecraft move further from the Earth, the signal
Speaker 1: strength will decrease. In fact, you know, here on Earth
Speaker 1: we describe radio frequencies as obeying the inverse square law,
Speaker 1: which means that the power of a signal is inversely
Speaker 1: proportional to the distance from a source. Hey, it's Jonathan
Speaker 1: from one day further out from when this episode originally published. Okay,
Speaker 1: so the first time I tried to explain this, I
Speaker 1: just playing god it all wrong. Uh, we published the episode,
Speaker 1: they had an error in it, and this was because
Speaker 1: of a fundamental misunderstanding on my part. But fortunately Charlie
Speaker 1: Tango Bravo on Twitter set me straight and I'm gonna
Speaker 1: try harder to get it right this time. So the
Speaker 1: inverse square law will first imagine that you have a
Speaker 1: source of electro magnetic radiation. And this can be anything
Speaker 1: from you know, a radio antenna to a microwave source
Speaker 1: to light. In fact, let's talk about light because that's
Speaker 1: pretty easy for us to wrap our heads around it
Speaker 1: because we can directly observe it. Right, We've all seen
Speaker 1: that as you move away from a source of light,
Speaker 1: then you get less light to work with, Right, that's intuitive.
Speaker 1: So if you're walking around I don't know, a spooky
Speaker 1: attic and it's lit by a single light bulb hanging
Speaker 1: down from a chain, well you know that as you
Speaker 1: get towards the corners, a ghost is gonna get you.
Speaker 1: I'm kidding. Ghosts don't exist, but you do know that
Speaker 1: as you move further away from the light, bulb, it
Speaker 1: gets darker, Right, That just something we've experienced. Well, we
Speaker 1: can actually describe this phenomena with the inverse square law
Speaker 1: of propagation. We can think of radiation moving out from
Speaker 1: a source as similar to that of an expanding sphere,
Speaker 1: like it's going out in all directions and growing as
Speaker 1: it moves outward. Right, the sphere gets bigger and bigger.
Speaker 1: The center is still stationary in this frame of reference.
Speaker 1: So the further we get out from the center of
Speaker 1: the sphere, the more surface area that electromagnetic radiation is covering. Right,
Speaker 1: the the outside of the sphere is bigger. That means
Speaker 1: that the signal strength is growing weaker. You have the
Speaker 1: same amount of signal to go around, but you're covering
Speaker 1: a larger area, so you can think of it as
Speaker 1: spreading across more space. And we can describe the relationship
Speaker 1: between signal intensity and distance as intensity equals one divided
Speaker 1: by r, that being the distance squared. So if you
Speaker 1: double the distance between you and a source, if you
Speaker 1: make are twice as big, the intensity you observe will
Speaker 1: drop by a factor of four. So if you went
Speaker 1: from one to two, then the intensity would go down
Speaker 1: to a quarter of what it used to be, you've
Speaker 1: reduced it by a factor of four. If you were
Speaker 1: to triple the distance between you and the source, then
Speaker 1: the intensity would reduce by a factor of nine. Three
Speaker 1: squared is nine, and so on and so forth. So
Speaker 1: I described in the previous version that signal does decrease
Speaker 1: as distance increases. That part was right, but the relationship
Speaker 1: I got totally wrong. The important thing to remember is
Speaker 1: that the signal strength drops off as we get further
Speaker 1: away from the source. So for spacecraft that are traveling
Speaker 1: further from Earth, that's a big factor we have to
Speaker 1: take into consideration. All right, let's get back to the
Speaker 1: original episode, and again, thank you to Charlie Tango Bravo
Speaker 1: for setting me on the right path. I appreciate it.
Speaker 1: And we also have to remember that there's a lot
Speaker 1: of stuff that generates radio signals. I mean, there's a
Speaker 1: ton of stuff here on Earth that we create, like
Speaker 1: TV and radio and cell phones and that kind of stuff.
Speaker 1: Those generate radio signals. But they're also a lot of
Speaker 1: things in space that generate radio signals, like pulsars and
Speaker 1: nebula and quasars. So in other words, there's a lot
Speaker 1: of potential noise to deal with when we're looking for
Speaker 1: a radio signal. So again, finding that that signal amid
Speaker 1: all the noise is a big challenge. It doesn't it's
Speaker 1: not just important that our antenna is sensitive. We have
Speaker 1: to have it really directional so that we can make
Speaker 1: certain that we're pointing at the thing we want to
Speaker 1: to listen to. Otherwise we might mistake some errant Earth
Speaker 1: generated signal as being our spacecraft and then we're on
Speaker 1: the wrong track. So to meet these challenges, NASA, through
Speaker 1: the JPL, established the Deep Space Network or d s N.
Speaker 1: The DSN has three facilities that are approximately a hundred
Speaker 1: twenty degrees apart in longitude, so that means they're roughly
Speaker 1: equidistant from each other Longitudinally, you multiply one twenty by three,
Speaker 1: you get three sixty. That's a circle, right. So one
Speaker 1: of the three is in Goldstone, California. That's actually in
Speaker 1: the desert. It's northeast of Los Angeles, it's south of
Speaker 1: Death Valley, and it's pretty far away from stuff that
Speaker 1: generates radio waves. The second is in Madrid, Spain, so
Speaker 1: that's almost smack dab in the middle of Spain. The
Speaker 1: third is in Canberra, Australia, which is on the coast
Speaker 1: in the southeast of Australia, and it's probably covered with
Speaker 1: venomous animals. I mean it's Australia, so it's a safe bet.
Speaker 1: So again, because these sites are a hundred twenty degrees
Speaker 1: apart from each other, we get that three hundred sixty
Speaker 1: degree view if you will, of the space around Earth.
Speaker 1: And what this means is that at any given time,
Speaker 1: at least one of the three DS insights has the
Speaker 1: ability to establish a line of sight communication channel with
Speaker 1: a distant spacecraft. And as the world rotates and one
Speaker 1: of these sites begins to lose contact, the next one
Speaker 1: will pick it right up, so communications can remain online.
Speaker 1: You don't have an interruption. This is a big thing.
Speaker 1: Like you might remember when I was talking about space stations.
Speaker 1: When the most recent as of this recording, anyway, when
Speaker 1: the most recent module joined the International Space Station, it
Speaker 1: was the Naka from the from Russia. When it docked,
Speaker 1: its thrusters misfired. They weren't supposed to fire, but they did,
Speaker 1: and it caused the space station to rotate and move
Speaker 1: into the wrong orientation relative to the Earth. Well, when
Speaker 1: that happened. The space station was not in range of
Speaker 1: Russia's mission control because that was on the wrong side
Speaker 1: of the Earth at the time, and that was a
Speaker 1: problem because Russia was the only entity that had the
Speaker 1: ability to control the thrusters on the Knocka. So that's
Speaker 1: an example of why it's important to have established these
Speaker 1: points where we can have uninterrupted contact. All right, we've
Speaker 1: got more to say about navigation, but before I get
Speaker 1: totally lost, let's take another quick break. So at these
Speaker 1: different sites at Goldstone, California, and Madrid, Spain, Canberra, Australia,
Speaker 1: they have a series of radio telescopes, including one really
Speaker 1: big one at each of these sites, and the deep
Speaker 1: space radio antenna can be extremely impressive. So the Goldstone
Speaker 1: Mars dish, that's the biggest one at gold Stone, California.
Speaker 1: That one was built in nineteen but it was later
Speaker 1: upgraded in night so today it measures seventy eaters across,
Speaker 1: that's about two thirty feet. Now, this dish has a
Speaker 1: surface area of around an acre or square feet or
Speaker 1: three thousand, eight hundred fifty square meters. It weighs nearly
Speaker 1: three thousand tons. It's mounted on massive machinery that can
Speaker 1: tilt and turn the dish so that it can be
Speaker 1: aimed precisely where a spacecraft is overhead and get you know,
Speaker 1: that laser like focus with a communications channel with a
Speaker 1: spacecraft that could be millions or billions of miles from
Speaker 1: the Earth. And the purpose of those big big dishes,
Speaker 1: I mean, it's all about collecting the very weak radio
Speaker 1: energy that's being sent back from the spacecraft. You know,
Speaker 1: because again that distances is intense, like the signals are
Speaker 1: very very weak by the time they get back to Earth,
Speaker 1: especially for super distant spacecraft. So this big dish is
Speaker 1: able to like that energy and then direct it toward
Speaker 1: the antenna itself, so you can think of it this parabola.
Speaker 1: It's all focusing that radio energy to a specific point,
Speaker 1: that point being the end of the actual radio antenna.
Speaker 1: Otherwise the signal would be so weak that it would
Speaker 1: be difficult, if not impossible, to detect that signal through
Speaker 1: all the noise, and engineers have to position and antenna
Speaker 1: precisely to beam radio instructions back to the distant spacecraft.
Speaker 1: If you're off even by a little bit, the message
Speaker 1: is not going to end up going to where you
Speaker 1: need it to. Go, and the further out the spacecraft
Speaker 1: is from Earth, the more critical it becomes to get
Speaker 1: that just right. So all of that is to set
Speaker 1: up the actual talk about navigation itself. We had to
Speaker 1: set all those parameters to talk about the process. Without
Speaker 1: the system like the Deep Space Network in place to
Speaker 1: communicate with spacecraft navigation would be impossible. We would not
Speaker 1: be able to build a spacecraft capable of detecting its
Speaker 1: own orientation and velocity and to make changes on the fly.
Speaker 1: It's not like Star Trek or Star Wars, where you
Speaker 1: just tell an on ship computer to plot a course
Speaker 1: for Javin or whatever. NASA describes space navigation as being
Speaker 1: the domain of three large departments within NASA. There's mission design,
Speaker 1: there's orbit determination, and there's flight path control. These three
Speaker 1: things all inter relate to one another. So first we
Speaker 1: have mission design. Now, this is the part of navigation
Speaker 1: in which mission control has to determine what the intended
Speaker 1: trajectory is for the spacecraft, where is it supposed to go. Now,
Speaker 1: this alone is tricky for all the reasons that I've
Speaker 1: talked about earlier in this episode. You've got to take
Speaker 1: all those different elements into consideration, like relativity. You know,
Speaker 1: what is it that you're hoping to do? What what
Speaker 1: is the purpose of the spacecraft? What are the things
Speaker 1: that are going to affect the spacecraft as it travels
Speaker 1: from Earth to get to where it's supposed to go.
Speaker 1: How do you account for those things? And how do
Speaker 1: you either incorporate stuff so that it, you know, it
Speaker 1: becomes part of your mission, or how do you find
Speaker 1: a way around an obstacle or challenge. Now, keep in mind,
Speaker 1: we learn new stuff the more we send spacecraft up,
Speaker 1: Like we learn more every single time, and some of
Speaker 1: that stuff is important and it affects calculations, like important
Speaker 1: for the sense of navigation, that is, it's always important.
Speaker 1: Someone has to take the things we've learned and then
Speaker 1: build that into software that we use to calculate complex
Speaker 1: equations in order to plot out navigation. So space navigation
Speaker 1: is something that has evolved over time, and as we
Speaker 1: learn more and incorporate what we've learned into the next
Speaker 1: generation of software, it's constantly in a state of change.
Speaker 1: So one thing that engineers have to factor in is
Speaker 1: the fact that a spacecraft is always orbiting. Something I
Speaker 1: kind of indicated this at the top of the show.
Speaker 1: You know, it could orbit the Earth. It could be
Speaker 1: in low Earth orbit and just stay there, but it's
Speaker 1: in orbit. Or you might want it to leave Earth
Speaker 1: orbit and enter into a solar orbit, so now it's
Speaker 1: orbiting the Sun just like Earth or Mars, or you know,
Speaker 1: any of the other planets are. Maybe you want to
Speaker 1: enter into a different planets orbit. Maybe you want it
Speaker 1: to leave the Solar System entirely, in which case it's
Speaker 1: in a galactic orbit. It's orbiting the center of the
Speaker 1: Milky Way, just like our Solar system is. It does
Speaker 1: require an awful lot of velocity in order to escape
Speaker 1: the Solar System. By the way, but we have done it,
Speaker 1: not with you know, humans obviously, but with spacecraft we've
Speaker 1: sent out anyway. Orbits are a huge part of navigation calculations.
Speaker 1: And again you're talking about an origin and a destination,
Speaker 1: and that are from an outside reference both in motion,
Speaker 1: and we have to take into account the effects of
Speaker 1: stuff like relativity with spacecraft. That's going to affect things
Speaker 1: like the clocks on board the spacecraft. That means we
Speaker 1: have to account for those changes due to relativity or
Speaker 1: else we risk losing track of the spacecraft. We might
Speaker 1: point an antenna at where a spacecraft either used to
Speaker 1: be or might be in the future, but isn't right now,
Speaker 1: just because we have these deviations from between our earthbound
Speaker 1: clocks and the ones that are aboard the spacecraft. So
Speaker 1: the software has to plot a trajectory that has to
Speaker 1: take all these different things into consideration, and as you
Speaker 1: can imagine, this means those calculations get pretty darn complicated,
Speaker 1: particularly when you're looking at something you know, really ambitious,
Speaker 1: which sounds a little weird to say, because I still
Speaker 1: think just getting something into low Earth orbit is being
Speaker 1: really ambitious. But you know, there's there is a scale,
Speaker 1: I guess, and as I'm sure we're all aware, software
Speaker 1: does not always come out perfect, right. You've probably used
Speaker 1: software where you've encountered a bug or a glitch, Like
Speaker 1: maybe you're playing a video game and the textures failed
Speaker 1: to load and everything looks weird. Well, that's irritating when
Speaker 1: it's a video game, but when you're talking about like
Speaker 1: interplanetary navigation, a bug or glitch can become an enormous challenge. Now,
Speaker 1: it might not be a show stopper. You might be
Speaker 1: able to work around it, but it likely will require
Speaker 1: a lot of people to work out a solution on
Speaker 1: the fly in order to make a sure that a
Speaker 1: spacecraft's route is in fact the right one to do
Speaker 1: whatever it is you want that spacecraft to do, all right. So,
Speaker 1: once all of that has been taken into account, engineers
Speaker 1: calculate the navigational route for a spacecraft. This planned route
Speaker 1: is the reference trajectory, so this is the route the
Speaker 1: spacecraft should be on. Also, there's a cesall relationship between
Speaker 1: the navigator for a mission and the software developers who
Speaker 1: are making the navigation software. So as navigators find bugs
Speaker 1: or they encounter new situations that necessitate new features in
Speaker 1: the software, they can relay that to the developers, and
Speaker 1: then they take the feedback and they produce new versions
Speaker 1: of the software. I imagine that gets increasingly challenging to do,
Speaker 1: especially to incorporate new features. Any developer can tell you
Speaker 1: that it can be a nightmare to put something new
Speaker 1: into code that you've just gotten to work, because the
Speaker 1: chances are you're going to break something that previously had
Speaker 1: been working. Okay, just imagine that for things that are
Speaker 1: traveling through space and you have to deal with relativity
Speaker 1: and stuff. Now, even when you do that correctly, which
Speaker 1: you know obviously requires a lot of work. It does
Speaker 1: not mean that a spacecraft is just going to magically
Speaker 1: stick to that reference trajectory. All sorts of things can
Speaker 1: cause the spacecraft to deviate from the planned route. In
Speaker 1: some cases, it might be on purpose us such as
Speaker 1: you know, you might have to do a maneuver to
Speaker 1: avoid a potential collision. Or it might be that your
Speaker 1: pathway is taking you close to a planet and you're
Speaker 1: planning on using a gravity assist two make the spacecraft
Speaker 1: continuance journey. But in other cases, something might pop up
Speaker 1: that wasn't anticipated, Like it happens very quickly. Maybe the
Speaker 1: spacecraft passes some large asteroids and the gravitational attraction between
Speaker 1: the spacecraft and the asteroids pulls the craft out of
Speaker 1: its trajectory a bit. Or maybe it turns out that
Speaker 1: the software had a bug in it or a blind
Speaker 1: spot that failed to account for something, and the spacecraft
Speaker 1: is veering off course a bit as a result. I mean,
Speaker 1: even solar pressure, that is pressure from light itself hitting
Speaker 1: the spacecraft can be enough to push the spacecraft off
Speaker 1: its reference trajectory. This is where orbit determination comes in. Now,
Speaker 1: as the name implies, this part of space navigation is
Speaker 1: just keeping track of a spacecraft's actual position. We know
Speaker 1: where we want the spacecraft to go, but this is
Speaker 1: about us figuring out where the spacecraft actually is. And
Speaker 1: that is another kittle of fish. NASA breaks down orbit
Speaker 1: determination into three sub processes or subgroups, So there's orbit reconstruction.
Speaker 1: This is asking the question where has this spacecraft been?
Speaker 1: This is all about determining the past route, the past
Speaker 1: locations for the spacecraft to understand its actual trajectory versus
Speaker 1: the reference trajectory. Then you've got orbit determination. This is
Speaker 1: like asking where the heck is the ding dang thing
Speaker 1: right now? Then you've got orbit prediction. This is like
Speaker 1: asking where the heck is this thing going to next?
Speaker 1: And and at this point I kind of wish I
Speaker 1: hadn't burned the mean Girls reference about gettin loser we're
Speaker 1: going shopping, But I did that one already. Anyway, A
Speaker 1: bit of consideration reveals that all three of these things
Speaker 1: are important. See, we're not controlling these spacecraft in real time.
Speaker 1: You know, you don't have someone sitting looking at a monitor.
Speaker 1: They get a first person view of a spacecraft's viewscreen.
Speaker 1: They've got a joystick and they're just making it fly
Speaker 1: all over the place. That's not how this works. And
Speaker 1: it does take time for a signal to pass from
Speaker 1: one point in space to another. The fastest that this
Speaker 1: can happen at is the speed of light, and you know,
Speaker 1: light is wicked fast. It's in fact the fastest stuff
Speaker 1: there is. But light can't traverse great distances in an instant.
Speaker 1: I mean it takes about eight minutes for light to
Speaker 1: go from the Sun to hit us here on Earth.
Speaker 1: So as as spacecraft gets further from the Earth, the
Speaker 1: information that we get back from those spacecraft becomes more dated. Right,
Speaker 1: it's more about where the space was at the time
Speaker 1: it transmitted, but minutes have passed between then and when
Speaker 1: we're able to actually look at the data. So as
Speaker 1: engineers get the latest telemetric data, they're actually looking at
Speaker 1: stuff that's several minutes old. So we're not observing the
Speaker 1: spacecraft directly. We're getting information back from the spacecraft, and
Speaker 1: then we have to draw conclusions about what's going on
Speaker 1: based upon the information we have. So if the data
Speaker 1: indicates that perhaps a ship is drifting away from its
Speaker 1: reference trajectory, we need to be able to look back
Speaker 1: and see what the data has said about that. When
Speaker 1: did that deviation begin? How long has it been going on?
Speaker 1: Where is the spacecraft now? Based on the information we have,
Speaker 1: keeping in mind we're projecting forward a few minutes because
Speaker 1: the information we have is older. And then, knowing that
Speaker 1: our ability to pinpoint a spacecraft position with precision decreases
Speaker 1: the further out the spacecraft gets from us, we have
Speaker 1: to start building in margins of error, and then, based
Speaker 1: upon all we know, where is it heading to now
Speaker 1: and how can we get it back on track? If
Speaker 1: we were not able to determine this, we wouldn't know
Speaker 1: where to point the antenna with the d s N
Speaker 1: in order to track the spacecraft. We would lose the spacecraft,
Speaker 1: let alone being able to figure out how to correct
Speaker 1: its its course. And you know space is big, so
Speaker 1: if you lose something like a spacecraft, good luck finding
Speaker 1: it again, because you'd you'd just be scanning regions of
Speaker 1: space looking for the faintest of radio signals to try
Speaker 1: and get back on track. It's not something you want
Speaker 1: to have happen. Well, we've got some more to talk
Speaker 1: about with navigation before we wrap all this up, So
Speaker 1: let's take one last break. Okay, I was talking about
Speaker 1: orbit re construction before the break, and we also need
Speaker 1: to reconstruct the path of the spacecraft in order to
Speaker 1: make sure that the scientific data that we're collecting with
Speaker 1: this satellite. I mean, presumably we've sent it up there
Speaker 1: to do something, well, some of it is determined by
Speaker 1: the trajectory path, Like we have to know the trajectory
Speaker 1: path in order for the data to make sense. There's
Speaker 1: imaging data. There's like a type of imaging called synthetic
Speaker 1: aperture radar imaging, and that requires that we have a
Speaker 1: precise knowledge of the spacecraft's trajectory so that the software
Speaker 1: we use to process that information can create a meaningful
Speaker 1: image from that data. Like it's not like it's sending
Speaker 1: a JPEG to us. It's sending us data that we
Speaker 1: then use to create an image with sophisticated software we
Speaker 1: have running on computers here on Earth. If we don't
Speaker 1: know the trajectory precisely, then it's almost like we're building
Speaker 1: a picture, but we're doing it from the wrong perspective,
Speaker 1: and it would leave us with an image that's nothing
Speaker 1: like what we were actually trying to capture with the satellite.
Speaker 1: So it is imperative that we know the actual trajectory
Speaker 1: of a spacecraft. Then we have flight path control, the
Speaker 1: third of the three departments I was talking about. Again,
Speaker 1: you could probably guess what this is about based on
Speaker 1: the name. We can summarize this by saying that this
Speaker 1: is the part of space navigation where we figure out
Speaker 1: how to get the spacecraft from where it actually is
Speaker 1: to where it is supposed to be. How can you
Speaker 1: get the spacecraft to return to the reference trajectory that
Speaker 1: you had set in the beginning. And here's another good
Speaker 1: reason to put so much emphasis on orbit determination, because
Speaker 1: spacecraft have a very limited set of options that they
Speaker 1: can use in order to return to the correct course.
Speaker 1: An interplanetary spacecraft, like a satellite that's designed to fly by, say,
Speaker 1: one of Saturn's moons, it needs to on course once
Speaker 1: it separates from the launch vehicle. You know, once it
Speaker 1: separates from the rocket that pushes it up into space.
Speaker 1: So this is kind of like a bowler releasing a
Speaker 1: bowling ball. You know, once that ball leaves your hand,
Speaker 1: there ain't no amount of you waving or leaning that's
Speaker 1: really going to affect the ball's trajectory. You've set it
Speaker 1: on a path and you can't really influence it anymore. Well,
Speaker 1: we can still influence spacecraft a little bit, but that
Speaker 1: initial release from the launch vehicle is the primary thing
Speaker 1: of putting it on its proper trajectory. So spacecraft can
Speaker 1: have like thrusters or rocket engines that can fire to
Speaker 1: adjust their course a little bit. But obviously there's actually
Speaker 1: a limit to how much fuel any spacecraft is able
Speaker 1: to carry. And there ain't no gas stations in space,
Speaker 1: at least not in our neighborhood. So fuel is a
Speaker 1: limited resource. And that's you know, an understatement, but it's
Speaker 1: important to remember. So let's say a spacecraft has gone
Speaker 1: a little bit off course. The flight path control group
Speaker 1: then has to figure out how far off course is it.
Speaker 1: Then they have to figure out the commands needed to
Speaker 1: have the spacecraft returned to its reference trajectory. So they
Speaker 1: take the data from the orbit determination group that tells them, okay,
Speaker 1: how far off course are we. Then they start running
Speaker 1: the calculations how much is it going to take for
Speaker 1: us to get back to where we need to be? Uh?
Speaker 1: This means figuring out the proper change in velocity for
Speaker 1: the spacecraft and if it's been a while since you've
Speaker 1: had physics, I want to remind you that velocity isn't
Speaker 1: just speed. A lot of folks use the word velocity
Speaker 1: to stand in for speed, but that's just part of it.
Speaker 1: Velocity is a vector. So in addition to speed, we
Speaker 1: have to have a direction. So a change in velocity
Speaker 1: is an acceleration. It can be a change in speed
Speaker 1: or direction or both. The flight path control team figures
Speaker 1: out what change in velocity is necessary, so they indicate
Speaker 1: the magnitude and the direction that is required in order
Speaker 1: for the spacecraft to return to its reference trajectory. Now,
Speaker 1: the flight path control team doesn't initiate the actual maneuver.
Speaker 1: They just designed the maneuver, or at least they design
Speaker 1: the parameters of the maneuver. It needs to have this
Speaker 1: change in direction and this magnitude. They send that information
Speaker 1: to another team, a spacecraft engineering team, and it's this
Speaker 1: group that then use stuff like attitude control systems and
Speaker 1: thrusters or rocket engines to produce the change in velocity
Speaker 1: that was indicated by the flat flight path control teams. So,
Speaker 1: in other words, they're the ones to take this data
Speaker 1: that says, here's what we need to have happen, and
Speaker 1: they're the ones to actually activate the systems to make
Speaker 1: it happen. NASA refers to small flight path control maneuvers
Speaker 1: as trajectory correction maneuvers, which makes sense. You're trying to
Speaker 1: correct it move it back to its reference trajectory. Now,
Speaker 1: as we conduct more space exploration, we learned things that
Speaker 1: are really able for future missions. So, for example, if
Speaker 1: we were to plot out a fly by satellite to
Speaker 1: go to Saturn, we would incorporate some gravity assist fly by.
Speaker 1: It's most likely this is where you leverage the gravitational
Speaker 1: pull of celestial body like another planet, to assist the
Speaker 1: spacecraft on its way by giving it kind of a
Speaker 1: slight pull slash push towards its destination and a change
Speaker 1: in velocity. It's a boost, kind of like someone giving
Speaker 1: you a little push when you're swinging on a swing set,
Speaker 1: although it can also you know, change your direction somewhat.
Speaker 1: And as we understand these things and we're able to
Speaker 1: build it in, we can have that planned from the beginning,
Speaker 1: so we can build them into an actual mission. When
Speaker 1: we've got a good handle on those things, NASA can
Speaker 1: call any sort of velocity maneuvers that we know we're
Speaker 1: going to have to do deterministic. That is, we have
Speaker 1: already determined the velocity maneuvers that we will need to
Speaker 1: conduct in order to maintain our reference true jectory given
Speaker 1: the route that we're following. We know that they are
Speaker 1: going to be maneuvers necessary to stay on course, and
Speaker 1: we have a good idea of what they are and
Speaker 1: when we will need to execute them. But there are
Speaker 1: other types of maneuvers that will call stochastic. These are
Speaker 1: maneuvers that we know we're gonna need to make, but
Speaker 1: we don't necessarily know. More like, we don't know what
Speaker 1: the magnitude of those changes might have to be. We
Speaker 1: might not fully understand the effect of those maneuvers ahead
Speaker 1: of time, because we're going through uncharted ground, if you
Speaker 1: if you will. We're not following something that we've already done,
Speaker 1: where we already kind of have a grasp on what
Speaker 1: we need to do. And then, of course occasionally sometimes
Speaker 1: we have to do these maneuvers when something we didn't
Speaker 1: anticipate at all happens and we have to design and
Speaker 1: conduct a maneuver kind of on demand. Also, I should
Speaker 1: mention that attitude control I mentioned it earlier Attitude control
Speaker 1: is not about whether or not you're spacecraft is sassin you.
Speaker 1: It has nothing to do with sass. Attitude refers to
Speaker 1: the angular orientation of a spacecraft given some other point
Speaker 1: of reference. Again, you have to have a point of reference,
Speaker 1: because I mean, if you think about it, outer space
Speaker 1: doesn't really have an up or down. You have to
Speaker 1: have a point of reference and compare your position to
Speaker 1: that point of reference, or you have to, you know,
Speaker 1: use your point of reference to in order to make
Speaker 1: a determination about something's positions. So you've gotta have a
Speaker 1: point of reference to start from in order for you
Speaker 1: to say something like that durned things upside down or
Speaker 1: backwards or you know, or whatever. Also, there are interesting
Speaker 1: ways to change the angular orientation of a spacecraft, and
Speaker 1: some of them do not involve thrusters or rocket engines. Instead,
Speaker 1: they might involve something like momentum wheels, as in, you know,
Speaker 1: physical wheels a rotor spun by a motor. Now I
Speaker 1: would get into this further, but that requires a pretty
Speaker 1: long discussion about things like the conservation of momentum and
Speaker 1: equal and opposite reactions and stuff like that, and we
Speaker 1: don't really have time for that this episode. Is already
Speaker 1: going super long, and I don't want Tardy to hate
Speaker 1: me more than she does already. So she doesn't hate me, folks,
Speaker 1: She's super nice to me. I just want to make
Speaker 1: that clear. That was more of a jest. But the
Speaker 1: short version of all this is that using stuff like
Speaker 1: momentum wheels can make it possible to change the attitude
Speaker 1: of a spacecraft without having to use thrusters. And as
Speaker 1: we've previously established, fuel is a precious resource. So that's
Speaker 1: a good thing to know, right to build in systems
Speaker 1: that allow us to make changes to a spacecraft's orientation,
Speaker 1: for example, without having to burn fuel to do it. Still,
Speaker 1: it's not uncommon that the spacecraft engineering team will actually
Speaker 1: have to initiate a rocket engine or a thruster ignition
Speaker 1: to provide the thrust needed to get back onto the
Speaker 1: reference trajectory. Uh, the timing on these maneuvers has to
Speaker 1: be incredibly precise, both because you don't want to waste
Speaker 1: even a drop of fuel if you can help it,
Speaker 1: and also that if you fire a thruster for too
Speaker 1: long or not long enough, then you're not going to
Speaker 1: return to your reference trajectory. So imagine, for a moment
Speaker 1: that you're sitting in mission control and you are relying
Speaker 1: on complex calculations from data sent back to you from
Speaker 1: space just to tell you where that something is right,
Speaker 1: and that's something the spacecraft is so far away that
Speaker 1: there is no means for us to observe it directly.
Speaker 1: All you have is the data coming back to go by,
Speaker 1: and then you have to come up with the command
Speaker 1: to send via radio back up to this object to
Speaker 1: get it back onto the course it's supposed to be
Speaker 1: following the data you have indicates that the thing you
Speaker 1: know was in this one particular position several minutes ago,
Speaker 1: So you have to figure out where it is now
Speaker 1: based on calculations with the data that you have, knowing
Speaker 1: that that is at best maybe a precise approximation, but
Speaker 1: still an approximation. Then you figure out the command you
Speaker 1: need to send to where the spacecraft is going to
Speaker 1: be in order to get it to take the action
Speaker 1: to get it to where it should be. This whole
Speaker 1: thing is mind boggling to me. It kind of makes
Speaker 1: me think of like submarine navigators who use precise charts
Speaker 1: and timing like a stop watch in order to plot
Speaker 1: underwater courses. Because they're not able to just look outside.
Speaker 1: I mean, at the depths that submarines can travel. You
Speaker 1: can't have windows because they would collapse in from the pressure.
Speaker 1: So you're in a tin can underwater, and you're using
Speaker 1: very precise maps and a stopwatch and knowledge of how
Speaker 1: fast you're moving in order to make calculations to determine
Speaker 1: whether or not you're going to bump into something. It's
Speaker 1: hard for me to even contemplate. Well, once the spacecraft
Speaker 1: engineering team has done their thing, that whole process has
Speaker 1: to repeat itself. The orbit determination team has to figure
Speaker 1: out if the spacecraft is in fact back on its
Speaker 1: reference trajectory, or if they'll need to conduct another maneuver,
Speaker 1: and so on and so forth. And because there's so
Speaker 1: many little things that can pull a spacecraft off track,
Speaker 1: this becomes a continuous process. It's incredible to me that
Speaker 1: people figured this stuff out, that they figured out how
Speaker 1: to not just not just how the universe works, Like
Speaker 1: it's already incredible to me that Einstein was able to
Speaker 1: determine these in incredible theories of special and general relativity,
Speaker 1: but then for people to build on that and to
Speaker 1: make technologies that take that into account, it's it's phenomenal.
Speaker 1: It also tells you by the way science works, right,
Speaker 1: because if science didn't work, the technology we build that
Speaker 1: leverages that science, it wouldn't work. So science works or
Speaker 1: else are tech wouldn't work, especially when it comes to
Speaker 1: space navigation. Now, there is a lot more that we
Speaker 1: could say about spacecraft navigation. I haven't really gone into
Speaker 1: deep details here, uh like how do you determine what
Speaker 1: a spacecraft's velocity is? For example? I haven't talked about
Speaker 1: that process, but I felt this was a good if
Speaker 1: you will high level overview of the topic. If you
Speaker 1: would like to know more details, let me know. I'll
Speaker 1: research and write and do a follow up episode and
Speaker 1: it will reference this one, but it will go into
Speaker 1: much more detail to talk about the actual processes and
Speaker 1: technologies we use to do the things I've talked about
Speaker 1: in this episode. If you want that episode or any
Speaker 1: other topic on tech Stuff, reach out to me on Twitter.
Speaker 1: That's the best way to get in touch with me.
Speaker 1: The handle we use for the show is tech Stuff
Speaker 1: H s W and I'll talk to you again really soon. Yeah.
Speaker 1: Text Stuff is an I Heart Radio production. For more
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